1. Field of Invention
The invention is a device to detect the start and end of injection as well as the injectate temperature during thermodilution determination of cardiocirculatory parameters and intra- and extravascular volumes.
2. Description of Related Arts
Cardiac Output (CO) and circulating blood volume are very important parameters to diagnose the condition of clinically ill patients. Measuring these parameters is a very important part of intensive care as well as in medical research. Such measurements are typically performed on critically ill patients in head surgical treatment and for pharmacological management strategies.
When employing a method of thermodilution for cardiac output determination, a liquid indicator colder than the blood temperature is injected into the right atrium or the superior or inferior vena cava. After a period of time, depending on the blood flow through the head and pulmonary circulation, a temperature drop can be detected in the femoral artery. By plotting the temperature drop over time, the area under the resulting curve can be used to determine cardiac output. To calculate cardiac output, it is crucial to know the exact temperature of the blood and the injected liquid. The blood temperature can be measured with an indwelling thermistor in the femoral artery, using a sensor that can be a temperature dependent resistor with a negative coefficient (NTC).
The temperature of the injected liquid is also measured with a resistor of the same type. This resistor is in thermal contact with the liquid within the injection channel. Hence, the temperature of the injected liquid can be measured during injection. In order to reuse the sensor, a thermal bridge is established between the sensor and the fluid path using a liquid impermeable material. This device is called IITS device (IITS) and is a sterile disposable item. The IITS is connected in series with the injection channel and contains the holder for the temperature sensor. Additionally, in this device includes a membrane as an actuator of a timing device. The defined time intervals on the indicator dilution curve allow calculation of intra- and extravascular volumes between site of injection and site of detection. However, precise detection of the start and finish of the injection is necessary.
Since determining these specific time points manually is impractical and imprecise, detection of a sudden step function of the temperature in the IITS is used. A sudden change in temperature is achieved by using cold injectate through the IITS that is at room temperature before injection. Consequently the injectate must be cooled prior to injection. This necessary step is a big disadvantage to the user in the intensive care unit, operating room or ambulance, where time may be a critical factor. Furthermore, providing cold injectate imposes not only additional labor time but may also introduce measurement errors and health risk to the patient. If the injectate is removed from the cooling compartment and injection is delayed, the liquid may warm up and may result in erroneous measurement. Additionally, if several consecutive determinations are performed, the IITS will cool and temperature detection will deteriorate.
The use of conventional cooling set at the bedside does not adequately address the above mentioned problems. The cooling set can only provide cold injectate provided that ice is constantly replenished in the cooler. The additional cooler also represents an added expense.
Because of the disadvantages mentioned above, the ability to use injectate at room temperature would simplify the measurement. Preferred embodiments of the present invention is a device that allows detection of the injectate temperature as well as beginning and end of injection at room temperature. More specifically, preferred embodiments of the present invention allows a user to detect the start and finish of injection for a thermodilution measurement at room temperature (approximately 20 degrees Celsius) without using cooled or heated injectate.